(1). Field of the Invention
The present invention relates to a novel curing agent for resins, a production process for the same and uses thereof, more specifically to novel polyaminoamide or novel ketimine obtained by dehydration-condensation of 2,5- and/or 2,6-bis(aminomethyl)-bicyclo[2,2,1]heptane (hereinafter abbreviated as NBDA) with carboxylic acids or ketones, a production process for the same and an epoxy resin composition or a urethane resin composition containing them.
(2). Description of the Related Art
Aliphatic polyamines such as ethylenediamine and hexamethylenediamine have so far been used widely for a curing agent for epoxy resins for the reasons that they have high curing rates and can cause curing at room temperature and that they are liquid and therefore easy to handle. In general, however, aliphatic polyamines have the defects that they have high vapor pressures at room temperature and have an unpleasant odor and strong skin stimulation. Further, since they are liable to absorb carbon dioxide in the air to bring about whitening, so-called amine brushing of a cured matter, an appearance of a cured resin is damaged in many cases. In addition thereto, physical properties of the resulting cured resin, such as flexibility, fastness to bend, impact resistance and adhesive property, and water resistance and chemical resistances such as acid resistance are not necessarily high to a sufficient extent. Further, while they have the advantage that they have a high reactivity and can cause fast curing, a principal component and the curing agent each have to be weighed just before using, and therefore they have had a large problem on workability. Naturally, it has never been possible to use them for applications of a one-component type resin in which a pre-mixture of a principal component and the curing agent is used for the sake of an enhancement in workability or for storage.
On the other hand, it is recognized that in general, alicyclic polyamines such as isophoronediamine and metaxylenediamine are advantageous from the viewpoint that they have lower vapor pressures and weak stimulation to skin as compared with aliphatic polyamines. However, the preceding defects of the aliphatic polyamines cannot completely be covered. It is shown in German Patent 3,202,491 that curing of a diglycidyl ether type resin of bisphenol with non-modified NBDA which is one of alicyclic polyamines proceeds rapidly at low temperature (50.degree. C. or lower) and the cured resin has a high acid resistance. However, if NBDA is actually used for a curing agent in a non-modified form, it produces almost the same defects as those of the aliphatic polyamines described above, and it is not suited for one-component type uses as it is.
While aromatic polyamines such as metaphenylenediamine and 4,4'-diaminodiphenylmethane have a small basicity and weak stimulation to skin, they have low curing rates, and the majority of them are solid at room temperature. Accordingly, they have the defects that the workability is inferior and it is difficult to handle them. Usually, they do not cause curing at room temperature, and therefore they are applied mainly to hot-setting uses.
Accordingly, improvement by various modifications of aliphatic or alicyclic polyamines are usually tried in order to solve these defects. It is described in, for example, Japanese Patent Application Laid-Open No. Sho 54-4992 that a suitable reactivity is provided when using for a curing agent for an epoxy resin a compound obtained by reacting 0.5 to 2.0 moles of a monoepoxy compound or an acrylic compound with 1 mole of NBDA and the resulting epoxy resin can be improved in physical properties. That is, these modified matters have the merit to retard curing at room temperature to improve the workability, and a coated film which is hot-set therewith is evaluated to have a good impact resistance, fastness to bend and chemical resistance.
However, while curing is retarded at room temperature, the resulting cured resin is insufficient in terms of gloss, water resistance and is chemical resistance and inferior in flexibility and an adhesive property. Further, while curing is retarded, it proceeds in due course, and therefore the above modifications can not be applied to a curing agent for one-component type resins in which principal components are blended in advance with the curing agent.
Some examples in which dicyandiamide, BF.sub.3 -amine complex, adipic acid hydrazide, imidazole derivatives and urea derivatives are used for one-component type latent curing agents for epoxy resins by blending in advance with epoxy resins are generally known, but they have the defect that heating at a high temperature for a long time is required for curing.
Curing agents making use of the fact that ketimines which are reaction products of amines with ketones isolate amines again by virtue of humidity (moisture) in the air are known as one-component type curing agents which are used by blending in advance with an epoxy resin. Use examples of the preceding curing agents for epoxy resins are described in Japanese Patent Publication No. Sho 38-20975 and Japanese Patent Application Laid-Open No. Sho 61-12723, but there have been the defects that the quick drying property, the adhesive property and the thick film-coating property are inferior for a curing agent and a multistage process is required in order to obtain ketimine having intended performances.
With respect to urethane resins, adhesives, sealants, coating agents and paints each using a one-component type humidity-curing urethane resin are used for architectural uses because of convenience thereof. One-component type humidity-curing urethane resins which have so far been available make use of a reaction of polyisocyanate with humidity (moisture), that is, a reaction in which a part of the polyisocyanate groups is turned into amine by decarboxylation of a reaction product of isocyanate with water and resulting amine is reacted with the balance of the polyisocyanate groups to cause curing. However, according to the reaction mechanism when this active isocyanate is reacted with water, carbon dioxide is generated. Accordingly, there have been some cases where resulting carbon dioxide is cut off from an escape and causes foaming in the inside depending on use and a coating method thereof. This foaming brings about reduced strength and inferior appearance to produce a large problem.